Question: If $3^{3x} = 81$, then what is the value of $x$? Express your answer as a common fraction.
Answer: We write 81 as a power of 3: $81=3^4$. Setting this equal to $3^{3x}$, we have $3^{3x} = 3^4 \Longrightarrow 3x=4$ and thus $x=\boxed{4/3}$.